The invention relates generally to methods and systems to prevent punch loss during automated sample processing.
Porous substrates, such as cellulose matrices (e.g. 31 ETF, FTA and FTA elute cards available from Whatman) are often used to store biological samples, such as blood. A new application area for these cards is in the pharmaceutical industry, which is using them to store dried blood samples from pharmacokinetic and toxicokinetic studies. When it is time to analyze the amount of drug or drug metabolite in the dried blood spot, the current methods require the user to cut the sample out of the card, usually a 1-6 mm diameter circle, place the cut disc in a vial or well with extraction fluid, and then shake/vortex for a set period of time. The extraction fluid is then removed and analyzed using a method such as LC-MS.
The pharmaceutical industry is expecting to process a large number of samples per day and is therefore looking for ways to automate the process. The current workflow of disc cutting and extraction, poses several problems when facing the challenge of automation. The primary problems arise from the cutting step. The small cut discs are highly prone to the effects of static electricity or even a light breeze. There are numerous reports of cut discs being lost during the cutting step or during transport of the cut discs. Currently, sample discs are lost due to factors such as static electricity and air movement. For example, static charges may build up in the plastic multiwall plates or tubes, causing the discs to sticks to the plates or tubes walls. The discs sometimes stick to the punching device or, later in the process, the discs sometimes stick to the liquid handling probes, which, when the probes are withdrawn from the well, the discs are inadvertently removed from the well.
The current instruments on the market focus on reducing sample disc loss by reducing the amount of air movement in the system (enclosed system) and adding anti-static devices (such as humidifiers).
Automated punching systems typically use a plate handling system (or tube strip handling system) that positions the plates/tubes below a stationary puncher so that each sample disc drops into a different well/tube. However, these plate-handling systems only move in two directions (forwards and sideways). This type of system leaves a gap between the bottom of the punching device and the top of the 96-well plate. The gap is necessary is such systems because the top of the plate would otherwise rub against the bottom of the punching device as it moves laterally from well to well.
Attempts have been made to use a modified plate cover to keep a punch inside a well, for example, by having small teeth on the cover of each well. However, this modification does not allow for liquids to subsequently be added to the wells with ease. Such modifications also do not allow the punch to be removed from, or otherwise moved within the well, once inserted into the well, which is important for some extraction methods. Other types of plate covers, for use on 96-well plates, are modified to prevent liquid from escaping from the well. These covers are thin films with slits cut into them to prevent evaporation and to allow small slow-moving probes, such as pipette tips or liquid handling probes, to enter the well. However, these thin films are quite stiff and intended to fully reseal as the pipettes are withdrawn from the wells. Such covers do not allow the punch to be inserted or otherwise moved within the receptacle without causing the punches to catch or otherwise stick onto top side of the covers or the ejector, and would necessarily require pipettes to add or remove any liquids from the wells in order to breach the sealed slits.